JP7524460B2 - Dual Input Image Light Guide - Google Patents

Description

The present invention relates to electronic displays, and more particularly to displays that use image light guides having diffractive optical elements to transmit image-bearing light to a viewer.

Head-mounted displays (HMDs) and virtual image near-eye displays are being developed for a variety of applications, including military, commercial, industrial, firefighting, and entertainment applications. In many of these applications, it is valuable to create a virtual image that can be visually superimposed on a real-world image in the HMD user's field of view. An optical image light guide delivers image-bearing light to the viewer within a small space and directs the virtual image to the viewer's pupil, making this superimposition possible.

While conventional image light guide structures have significantly reduced the bulk, weight, and cost of near-eye display optical systems, further improvements are needed. In some cases, the size of the eyebox is limited, which limits the movement tolerance and device placement tolerance in HMD designs. Light can often be unevenly distributed in the field of view, resulting in hot spots with high light levels in the center of the field of view and low light levels at the periphery. In some cases, the diffraction efficiency of the image light guide is not sufficient to produce the desired image brightness. The virtual image generated by the image light guide structure must have sufficient brightness for satisfactory visibility and viewer comfort.

In a first exemplary embodiment, the present disclosure provides an image light guide for transmitting a virtual image. The image light guide comprises a substrate operable to transmit an image-bearing light beam. A first incoupling diffractive optical element is formed along the substrate. The first incoupling diffractive optical element is operable to diffract a first portion of the image-bearing light beam from an image source into the substrate in an angularly encoded form and transmit a second portion of the image-bearing light beam from the image source. An outcoupling diffractive optical element is formed along the substrate. The outcoupling diffractive optical element is operable to expand the image-bearing light beam and direct the expanded image-bearing light beam from the substrate in an angularly decoded form. A second incoupling diffractive optical element is formed along the substrate. The second incoupling diffractive optical element is operable to diffract a portion of the second portion of the image-bearing light beam into the substrate in an angularly encoded form. The image light guide further comprises an optical coupler. The optical coupler is disposed along an axis of the image source and is operable to direct the second portion of the image-bearing light from the image source to the second incoupling diffractive optical element.

In a second exemplary embodiment, the present disclosure provides an image light guide system for transmitting a virtual image. The image light guide system includes an image source operable to project image-bearing light corresponding to a virtual image along a first axis. Pixels of the virtual image are focused at infinity. The image light guide system also includes a first substrate operable to propagate the image-bearing light and a second substrate operable to propagate the image-bearing light and coupled to the first substrate. Each of the first and second substrates includes a first incoupling diffractive optical element, a second incoupling diffractive optical element, and an outcoupling diffractive optical element. The outcoupling diffractive optical element is operable to magnify the image-bearing light and direct the magnified image-bearing light away from the substrate. The image light guide system further includes an optical coupler disposed along the first axis. The optical coupler is disposed at least partially along a path of the image-bearing light transmitted through the first incoupling diffractive optical elements of the first and second substrates. The optical coupler is operable to direct the image-bearing light to the second incoupling diffractive optical element of the second substrate. The second incoupling diffractive optical element is operable to diffract a portion of the image-bearing light into the second substrate in an angularly encoded manner and transmit a portion of the image-bearing light to direct it to the second incoupling diffractive optical element of the first substrate. The second incoupling diffractive optical element of the first substrate is operable to diffract a portion of the image-bearing light into the first substrate in an angularly encoded manner.

The accompanying drawings are incorporated herein as part of the detailed description. The disclosed drawings illustrate embodiments of the subject matter disclosed herein and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible embodiment of the subject matter disclosed herein and are not intended to limit the scope of the present disclosure.

FIG. 2 is a simplified cross-sectional view of an image light guide illustrating the expansion of an image-bearing beam along the propagation direction to expand in one direction of the eyebox.

FIG. 13 is a perspective view of an image light guide with a rotating grating illustrating the expansion of the image-bearing beam perpendicular to the propagation direction to expand the second direction of the eyebox.

1 is a plan view of an image light guide having two incoupling diffractive optical elements according to an exemplary embodiment of the disclosed subject matter.

4 is a side view of the image light guide of FIG. 3 having an optical coupler according to an exemplary embodiment of the present disclosure.

5 is an end side view of the image light guide of FIG. 4 having two incoupling diffractive optical elements disposed on a first surface.

5 is an end side view of the image light guide of FIG. 4 having a first incoupling diffractive optical element disposed on a first surface and a second incoupling diffractive optical element disposed on a second surface.

5 is an end side view of the image light guide of FIG. 4 having a first incoupling diffractive optical element disposed on the second surface and a second incoupling diffractive optical element disposed on the first surface.

5 is an end side view of the image light guide of FIG. 4 having a first incoupling diffractive optical element disposed on a second surface and a second incoupling diffractive optical element disposed on a second surface.

5 is a perspective view of the image light guide of FIG. 4.

FIG. 5 is a perspective view of the optical coupler of FIG. 4 .

5 shows an end face of the optical coupler of FIG. 4, where the first surface includes a mirror.

5 is an end side view of the image light guide of FIG. 4.

FIG. 8B is an end side view of the image light guide of FIG. 8A with the planar waveguide rotated about an axis.

FIG. 5 is a plan view of the optical coupler of FIG. 4 .

1A-1C illustrate a portion of a periodic grating according to an exemplary embodiment of the disclosed subject matter. 1A-1C illustrate a portion of a periodic grating according to an exemplary embodiment of the disclosed subject matter.

1 is an end side view illustrating a stacked image light guide system according to an exemplary embodiment of the disclosed subject matter.

FIG. 12 is a side view of the stacked image light guide system of FIG. 11.

FIG. 1 illustrates a display system for viewing augmented reality using an image light guide according to an exemplary embodiment of the subject matter of this disclosure.

It should be understood that the present invention may assume various alternative orientations and step sequences, unless expressly specified. It should also be understood that the specific assemblies and systems illustrated in the accompanying drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Thus, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered as limiting, unless specifically stated otherwise. Also, where not otherwise stated, similar elements in the various embodiments described herein are commonly referred to by similar reference numerals.

As used herein, the terms "first," "second," and the like do not necessarily denote any order, sequence, or priority relationship, but are merely used to clearly distinguish one element or set of elements from another, unless otherwise specified.

As used herein, the terms "viewer," "operator," "observer," and "user" are considered equivalent and refer to a person or machine that views an image using a device having an image light guide.

As used herein, the term "set" refers to a nonempty set, as commonly understood in elementary mathematics to refer to a collection of elements or members. As used herein, the term "subset," unless otherwise specified, refers to a nonempty proper subset, i.e., a subset of a larger set that has one or more elements. A subset may constitute the entire set S. However, a "proper subset" of a set S is a set that is entirely contained in set S but excludes at least one member of set S.

As used herein, the terms "coupled," "coupler," and "coupling" in the optical arts refer to coupling that transmits light from one optical medium or device to another.

As used herein, the terms "beam expansion," "expanding an image-bearing beam," and "expanded image-bearing light" refer to the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions. Similarly, as used herein, "expanding" a beam or a portion of a beam refers to the duplication of the beam through multiple encounters with optical elements to expand the exit pupil in one or more directions.

Optical systems such as HMDs can display virtual images. In contrast to real image projection, the virtual image is not projected onto the display surface. That is, if the display surface were in a position to perceive the virtual image, no image would be projected onto the display surface. In augmented reality displays, virtual image projection has a number of inherent advantages. For example, the apparent size of the virtual image is not limited by the dimensions or position of the display surface. Furthermore, the object that is the source of the virtual image can be small. For example, a magnifying glass provides a virtual image of an object. By projecting a virtual image that appears to be at some distance, a more realistic visual experience can be provided compared to systems that project real images. Furthermore, providing a virtual image eliminates the need to correct screen artifacts, which is necessary in the case of real image projection.

An image light guide can display a virtual image using image-bearing light from a light source such as a projector. For example, a collimated and relatively angularly encoded light beam from a projector is coupled into a planar waveguide by in-coupling, such as an in-coupling diffractive optical element, which is attached to or formed on the surface of the planar waveguide or embedded within the waveguide. Such a diffractive optical element can be formed as a diffraction grating, a holographic optical element (HOE), or in other known manner. For example, a diffraction grating can be formed by a surface relief. After the diffracted light propagates along the waveguide, it can be directed back out of the waveguide by a similar out-coupling, such as an out-coupling diffractive optical element. The out-coupling diffractive optical element can be positioned to provide pupil expansion along one direction. Additionally, a rotating grating can be placed on or within the waveguide to provide pupil expansion in an orthogonal direction. The image-bearing light output from the waveguide provides the viewer with an expanded eyebox.

As shown in FIG. 1, the image light guide 10 comprises a planar waveguide 22 having flat and parallel surfaces. The planar waveguide 22 comprises a transparent substrate S having an outer surface 12 and an inner surface 14 disposed opposite the outer surface 12. In this embodiment, an incoupling diffractive optical element IDO and an output coupling diffractive optical element ODO are disposed on the inner surface 14. The incoupling diffractive optical element IDO is a reflective diffraction grating through which the image-bearing light WI is coupled into the planar waveguide 22. However, the incoupling diffractive optical element IDO may be a transmission grating, a volume hologram or other holographic diffractive element, or any other type of optical element that diffracts the incoming image-bearing light WI. The incoupling diffractive optical element IDO may be disposed on the outer surface 12 or the inner surface 14 of the planar waveguide 22, and may be transmission or reflection, depending on the direction in which the image-bearing light WI approaches the planar waveguide 22.

When used as part of a virtual display system, the incoupling diffractive optical element IDO couples image-bearing light WI from an image source into the substrate S of the planar waveguide 22. The real or image dimension is first transformed into an array of overlapping angularly related beams that encode different locations within the virtual image presented to the incoupling diffractive optical element IDO. The image-bearing light WI is diffracted (approximately by first order diffraction) and thereby redirected by the incoupling diffractive optical element IDO into the planar waveguide 22 as image-bearing light WG, which is further propagated along the planar waveguide 22 by total internal reflection (TIR). The image-bearing light WG is diffracted into a more condensed range of approximately angularly related beams to meet the boundaries defined by the TIR, but retains the image information in an encoded form. The outcoupling diffractive optical element ODO receives the encoded image-bearing light WG and diffracts the image-bearing light WG as image-bearing light WO out of the planar waveguide 22 toward the intended position of the viewer's eye (again, approximately by first order diffraction). In general, the outcoupling diffractive optical element ODO is designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light WI in the angularly related beam of the output image-bearing light WO. However, in order to increase one dimension of the overlap of the angularly related beams in the so-called eyebox E where the virtual image can be seen, the outcoupling diffractive optical element ODO is configured to encounter the image-bearing light WG multiple times and diffract only a portion of the image-bearing light WG at each encounter. The multiple encounters in the propagation direction along the length of the outcoupling diffractive optical element ODO have the effect of expanding the eyebox E where the beams overlap in one direction. The expanded eyebox E reduces the sensitivity to the position of the viewer's eye for viewing the virtual image.

In this embodiment, the outcoupling diffractive optical element ODO is a transmissive diffraction grating disposed on the inner surface 14 of the planar waveguide 22. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be disposed on the outer surface 12 or the inner surface 14 of the planar waveguide 22, and may be transmissive or reflective in combination with the direction in which the image-bearing light WG is intended to exit the planar waveguide 22.

As shown in FIG. 2, the image light guide 20 can be configured to expand the eyebox 74 in two directions, i.e., along the x-axis and y-axis of the intended image. To achieve beam expansion in the second direction, the incoupling diffractive optical element IDO is oriented to diffract the image-bearing light WG with a grating vector k0 toward the intermediate rotating grating TG, whose grating vector k1 is oriented to diffract the image-bearing light WG in a reflective mode toward the outcoupling diffractive optical element ODO. Each of the many encounters with the intermediate rotating grating TG diffracts only a portion of the image-bearing light WG, thereby laterally expanding each angularly associated beam of image-bearing light WG approaching the outcoupling diffractive optical element ODO. The intermediate rotating grating TG redirects the image-bearing light WG into a direction that is at least approximately aligned with the grating vector k2 of the outcoupling diffractive optical element ODO. This is to longitudinally expand the angularly related beams of image-bearing light WG in a second direction before exiting the planar waveguide 22 as image-bearing light WO. The grating vectors, such as the depicted grating vectors k0, k1, k2, extend in a direction perpendicular to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optical element and have a magnitude that is inversely proportional to the period or pitch d (i.e., the center-to-center distance between grooves) of the diffractive optical elements IDO, TG, ODO.

As shown in FIG. 2, the incoupling diffractive optical element IDO receives an incoming image-bearing light WI. This image-bearing light W1 includes a set of angularly related beams that correspond to pixels or equivalent locations in an image generated by the image source 16. The image source 16 is operable to generate a range of angularly encoded beams to create a virtual image. The image source 16 can be, but is not limited to, a real image display used with focusing optics, a beam scanner to set the beam angle more directly, or a one-dimensional real image display combined with a scanner. The image light guide 20 outputs a set of angularly related beams expanded in two directions of the image by providing multiple encounters of the image-bearing light WG with the intermediate rotating grating TG and the outcoupling diffractive optical element ODO with different orientations. In the original orientation of the planar waveguide 22, the intermediate grating TG provides beam expansion in the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar beam expansion in the x-axis direction. The reflectivity characteristics and respective periods d of the diffractive optical elements IDO, ODO, and TG, and the orientation of their respective grating vectors, expand the beam in two directions while preserving the intended relationships between the angularly related beams in the image-bearing light WI, and output the beam from the image light guide 20 as image-bearing light WO.

Although the image-bearing light WI input to the image light guide 20 is encoded by the incoupling diffractive optical element IDO into a different set of angularly related beams, the information necessary to reconstruct the image is preserved by the systematic effect of the incoupling diffractive optical element IDO. The rotating grating TG is located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO and is typically configured so as not to cause a significant change in the encoding of the image-bearing light WG. The outcoupling diffractive optical element ODO is typically configured symmetrically with respect to the incoupling diffractive optical element IDO, e.g., including diffractive features that share the same period. Similarly, the period of the rotating grating TG also typically matches the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. As shown in FIG. 2, the grating vector k1 of the rotating grating is illustrated as being oriented at 45° with respect to the other grating vectors (all as unoriented line segments). However, in one embodiment, the grating vector k1 of the rotating grating TG is oriented at 60° relative to the grating vectors k0, k2 of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, and the image-bearing light WG is rotated by 120°. By orienting the grating vector k1 of the intermediate rotating grating TG at 60° relative to the grating vectors k0, k2 of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, the grating vectors k0, k2 of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO are also oriented at 60° relative to each other (again, the grating vectors are considered as unoriented line segments). Since the magnitude of the grating vector is based on the common pitch of the rotating grating TG, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO, the three grating vectors k0, k1, k2 as oriented line segments form an equilateral triangle, and the sum of the magnitudes is zero. This avoids asymmetric effects that may cause undesirable aberrations, including chromatic dispersion.

The image-bearing light WI diffracted into the planar waveguide 22 is effectively encoded by the incoupling diffractive optical element, whether the incoupling diffractive optical element is a grating, hologram, prism, mirror, or other mechanism. The reflection, refraction, and/or diffraction of light occurring at the incoupling diffractive optical element IDO must be decoded by the outcoupling diffractive optical element ODO to recreate the virtual image presented to the viewer. The rotating grating TG, preferably located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically designed and oriented so as not to cause any modification to the encoded light. The outcoupling diffractive optical element ODO decodes the image-bearing light WG into an angularly related beam of the original or desired shape, which is expanded to fill the eyebox 74.

Regardless of whether symmetry is maintained between the rotating grating TG and the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, and regardless of whether any changes occur along the planar waveguide 22 in the encoding of the angularly associated beams of the image-bearing light WI, the rotating grating TG and the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO are associated such that the image-bearing light WO output from the planar waveguide 22 maintains or preserves the original shape of the image-bearing light WI or a desired shape for generating the intended virtual image.

The letter "R" represents the orientation of the virtual image as seen by a viewer with eyes in the eyebox 74. As shown, the orientation of the letter "R" in the represented virtual image corresponds to the orientation of the letter "R" encoded in the image-bearing light WI. A change in the rotation or angular orientation of the incident image-bearing light WI about the z-axis in the x-y plane causes a corresponding symmetric change in the rotation or angular orientation of the light exiting the outcoupling diffractive optical element ODO. In terms of image orientation, the rotating grating TG simply acts as a kind of optical relay, expanding the angularly encoded beam of image-bearing light WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical element ODO expands the angularly encoded beam of image-bearing light WG along another axis of the image (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light WI. As shown in FIG. 2, the rotating grating TG is a tilted or square diffraction grating and is disposed on the front or rear surface of the planar waveguide 22. Alternatively, the rotating grating TG may be a blazed diffraction grating.

The present disclosure provides an image light guide configuration that improves the output intensity of image-bearing light passing through an output aperture. More specifically, the present disclosure provides, among other things, a waveguide having one or more incoupling and outcoupling diffractive optical elements operable to expand an image-bearing light beam in two directions and output the expanded image-bearing light beam toward an eyebox.

3, 4, and 5A, the image light guide 100 has a first incoupling diffractive optical element IDO1, a second incoupling diffractive optical element IDO2, and an outcoupling diffractive optical element ODO formed on the first surface 102 of the planar waveguide 22. In another embodiment, as shown in FIG. 5B, the first incoupling diffractive optical element IDO1 and the outcoupling diffractive optical element ODO are formed on the first surface 102 of the planar waveguide 22, and the second incoupling diffractive optical element IDO2 is formed on the second surface 104 (the surface opposite the first surface 102) of the planar waveguide 22. In another embodiment, as shown in FIG. 5C, the first incoupling diffractive optical element IDO1 is formed on the second surface 104 of the planar waveguide 22, and the second incoupling diffractive optical element IDO2 and the outcoupling diffractive optical element ODO are disposed on the first surface 102 of the planar waveguide 22. In another embodiment, as shown in FIG. 5D, the first and second incoupling diffractive optical elements IDO1, IDO2 are formed on the second surface 104 of the planar waveguide 22, and the outcoupling diffractive optical element ODO is disposed on the first surface 102 of the planar waveguide 22. In yet another embodiment, the first and second incoupling diffractive optical elements IDO1, IDO2 and the outcoupling diffractive optical element ODO are formed on the second surface 104 of the planar waveguide 22.

Referring to FIG. 3, in one embodiment, the first and second incoupling diffractive optical elements IDO1, IDO2 include two sets of periodic grating structures 106, 108. For example, the incoupling diffractive optical element IDO includes a first set of periodic linear grating structures 106 rotated/offset by an angle of less than 30 degrees (e.g., 25°) with respect to the x-axis, and a second set of periodic linear grating structures 108 rotated/offset by an angle of less than -30 degrees (e.g., -25°) with respect to the x-axis. The first set of periodic grating structures 106 and the second set of periodic grating structures 108 are intersecting. The first set of periodic grating structures 106 includes a first period, and the second set of periodic grating structures 108 includes a second period. In one embodiment, the second period is equal to the first period.

In one embodiment, the outcoupling diffractive optical element ODO comprises a third set of periodic grating structures 110 and a fourth set of periodic grating structures 112. The third and fourth sets of periodic grating structures 110, 112 are parallel to the first and second sets of periodic grating structures 106, 108, respectively. The third and fourth sets of periodic grating structures 110, 112 form a composite diffractive optical element operable to magnify and outcouple the image-bearing light from the incoupling diffractive optical elements IDO1, IDO2. In one embodiment, the third set of periodic grating structures 110 intersects with the fourth set of periodic grating structures 112. The third and fourth sets of periodic grating structures 110, 112 may also have the same periodicity as the first and second sets of periodic grating structures 106, 108, respectively. In one embodiment, the outcoupling diffractive optical element ODO is symmetrical across the longitudinal axis 115.

As shown in Figures 4-7B, in one embodiment, the image light guide 100 includes an optical coupler 120. The optical coupler 120 is adjacent to the incoupling diffractive optical elements IDO1, IDO2 and is positioned on the opposite side of the planar waveguide 22 from the projector 16 (i.e., the image source). In one embodiment, the optical coupler 120 includes a first face 122 located near the planar waveguide 22. The optical coupler 120 also includes a second face 124 disposed at an angle α relative to the first face 122 and a symmetric third face 126 disposed at an angle α relative to the first face 122. In one embodiment, the optical coupler 120 is assembled from two right angle prisms 120A, 120B. In one embodiment, the second and third faces 124, 126 are mirror surfaces.

The first surface 122 is an input surface of the optical coupler 120 and receives image-bearing light from the projector 16 along a first axis A1. The first axis A1 is aligned with the central ray of the projector 16. The image-bearing light is reflected at the second surface 124 back toward the first surface 122 within an angular range of TIR (total internal reflection). The first surface 122 is operable to reflect the image-bearing light in TIR, and the image-bearing light reflected from the second surface 124 is reflected by the first surface 122 toward a third surface 126. The third surface 126 further reflects the image-bearing light toward the first surface 122 within an angular range operable to transmit the image-bearing light through the first surface 122. The image-bearing light is output from the optical coupler 120 about a second axis A2. The second axis A2 is aligned with the central ray output from the optical coupler 120. The second axis A2 is offset from the first axis A1 in the y-axis direction. Designing the optical coupler 120 to have three reflection points within the optical coupler 120 prevents the virtual image of the image-bearing light entering the optical coupler 120 from flipping.

In operation, image-bearing light WI from projector 16 is incident on the first incoupling diffractive optical element IDO1, and a first portion WG1 of the image-bearing light is diffracted by the first incoupling diffractive optical element IDO1 and propagates by TIR towards the outcoupling diffractive optical element ODO. A second portion of the image-bearing light WI is transmitted through the first incoupling diffractive optical element IDO1 and the planar waveguide 22 and incident on the optical coupler 120. The second portion of the image-bearing light WI is transmitted through a first face 122 of the optical coupler 120 and reflected by a second face 124 of the optical coupler at an angle of incidence operable to reflect by the first face 122 by TIR. A second portion of the image-bearing light WI is then reflected by the first surface 122 in TIR and enters the third surface 126 of the optical coupler, where the second portion of the image-bearing light WI is reflected toward the first surface 122 and transmitted through the first surface 122 along the second axis A2.

A second portion of the image-bearing light WI, centered on the second axis A2, is then incident on the second incoupling diffractive optical element IDO2. A portion of the second portion WG2 of the image-bearing light is diffracted by the second incoupling diffractive optical element IDO2 and propagates toward the outcoupling diffractive optical element ODO via TIR. In one embodiment, the second incoupling diffractive optical element IDO2 is configured to optimize the diffraction efficiency of the image-bearing light output from the optical coupler 120. For example, the first incoupling diffractive optical element IDO1 is configured as a transmission type diffraction grating, and the second incoupling diffractive optical element IDO2 is configured as a reflection type diffraction grating. As shown in Figures 10A and 10B, when the first and second sets of periodic grating structures 106, 108 are surface relief gratings, the first and second sets of periodic grating structures 106, 108 are inclined at an inclination angle φ with respect to a plane parallel to the first and second faces 102, 104 of the planar waveguide 22. In one embodiment, the first set of periodic grating structures 106 of the first incoupling diffractive optical element IDO1 has a tilt angle φ ₁ , and the first set of periodic grating structures 106 of the second incoupling diffractive optical element IDO2 has a tilt angle φ _2. Similarly, the second set of periodic grating structures 108 of the first incoupling diffractive optical element IDO1 has a tilt angle φ ₁ , and the second set of periodic grating structures 108 of the second incoupling diffractive optical element IDO2 has a tilt angle φ _2. The periodic grating structures 106, 108 of the first and second incoupling diffractive optical elements IDO1, IDO2 have tilt angles φ rotated 180 degrees with respect to each other.

By utilizing optical coupler 120 and second incoupling diffractive optical element IDO2, image light guide 100 is operable to incouple a greater percentage of image-bearing light from projector 16. Increasing the percentage of image-bearing light from projector 16 that is incoupled into planar waveguide 22 increases the brightness of the virtual image seen in the eyebox.

In one embodiment, as shown in FIG. 7B, the first face 122 of the optical coupler 120 may include a mirrored surface 132. The mirrored surface 132 is formed on the first face 122 such that a second portion of the image-bearing light reflected from the second face 124 is incident on the mirrored surface 132. The mirrored surface 132 may be formed by applying an at least partially reflective coating to a portion of the first face 122 of the optical coupler. Image-bearing light from the image source 16 is incident on and transmitted through a first portion 122A of the first face 122 of the optical coupler and incident on the second face 124. The image-bearing light reflected from the second face 124 is incident on a second portion 122B of the first face 122 having the mirrored surface 132 and is reflected toward the third face 126. The image-bearing light reflected from the second portion 122B of the first surface 122 is incident on the third surface 126 and is reflected toward the third portion 122C of the first surface 122. The image-bearing light incident on the third portion 122C of the first surface 122 is transmitted therethrough.

In one embodiment, as shown in FIGS. 4, 5A-5D, and 7B, the image light guide 100 includes a waveplate 130 disposed between the optical coupler 120 and the planar waveguide 22. The length of the waveplate 130 is shorter than the optical coupler 120 such that light transmitted through the planar waveguide 22 and incident on the first face 122 of the optical coupler 120 does not pass through the waveplate 130, and image-bearing light reflected from the third face 126 and transmitted through the first face 122 of the optical coupler 120 passes through the waveplate 130. The waveplate 130 is operable to change the polarization direction of the image-bearing light from the projector 16 such that the image light guide 100 fully utilizes the image-bearing light from the projector 16. For example, the waveplate 130 may be a half-waveplate operable to rotate the polarization direction of the image-bearing light to or near a right angle (90°). In one embodiment, the wave plate 130 may be a quarter wave plate operable to rotate the polarization direction of the image-bearing light by approximately forty-five degrees (45°). A transmissive grating is less polarization sensitive than a reflective grating. If the second incoupling diffractive optical element IDO2 is a reflective grating, polarization of the image-bearing light through the half wave plate 130 allows for greater diffraction efficiency. In other words, in one embodiment, more image-bearing light from the image source 16 is available to incouple through the second incoupling diffractive optical element IDO2 with an alternate polarization into the waveguide 22. In one embodiment, the projector 16 comprises a digital light processing "DLP" projector operable to output unpolarized light.

In one embodiment, as shown in FIG. 8A, if the optical coupler 120 is imperfectly manufactured and/or if there is an error in the alignment of the projector 16 and the optical coupler 120, the image light guide 100 may generate two misaligned virtual images. For example, as shown in FIG. 8A, due to imperfections in the optical coupler 120, the image-bearing light WG2 may be incident on the second incoupling diffractive optical element IDO2 at an angle relative to the second axis A2. This angle of incidence is reflected in the angle of the second output light beam WO2 relative to the second axis A2, causing the two virtual images to be misaligned. As shown in FIG. 8B, the planar waveguide 22 can be rotated or swung about the x-axis and/or y-axis to align the two virtual images generated by the image light guide 100. Rotating the planar waveguide 22 relative to the projector 16 and the optical coupler 120 compensates for the effects of imperfections in the alignment of the central ray of the image-bearing light beam WG2 (the image-bearing light beam in-coupled into the planar waveguide 22 via the second incoupling IDO2 and out-coupled via the outcoupling diffractive optical element ODO). Rotating the planar waveguide 22 about the center of the first incoupling diffractive optical element IDO1 allows the second outgoing light beam WO2 to be repositioned relative to the second incoupling diffractive optical element IDO2 without changing the position of the central ray of the first outgoing light beam WO1 relative to the center of the first diffractive optical element IDO1. As shown in Figures 8A and 8B, rocking the planar waveguide 22 aligns the central rays of the image-bearing light beams WO1, WO2 approximately parallel to each other. This feature allows for a larger tolerance in the alignment of the projector 16 and the optical coupler 120. In other words, the projector 16 and the optical coupler 120 do not need to be very precisely aligned because the waveguide 22 can be used to align the virtual image.

11 and 12, in one embodiment, the stacked image light guide assembly 400 includes a first image light guide 402 coupled to a second image light guide 404. At least one of the first image light guide 402 and the second image light guide 404 is one of the image light guides 100 described above. The image light guides 402, 404 are formed on separate waveguide substrates 22 that are mechanically coupled. In one embodiment, the waveguide substrates 22 of the image light guides 402, 404 are mechanically coupled via an adhesive. In another embodiment, the waveguide substrates 22 are held in place relative to each other by structural means of the HMD. For example, if the HMD incorporating the image light guides 402, 404 are smart glasses (see FIG. 13), the substrates 22 can be held in relative position via the rims of the smart glasses. In one embodiment, the stacked image light guide assembly 400 provides three independent color channels. A first portion of the image-bearing light WI from the projector 16 that is incident on the first incoupling diffractive optical element IDO1 of the first image light guide 402 is diffracted and propagates via TIR towards the outcoupling diffractive optical element ODO of the first image light guide 402.

A second portion of the image-bearing light WI incident on the first incoupling diffractive optical element of the first image light guide 402 is transmitted therethrough and incident on the first incoupling diffractive optical element IDO1 of the second image light guide 404. A portion of the image-bearing light WG2 incident on the first incoupling diffractive optical element IDO1 of the second image light guide 404 is diffracted and propagates via TIR towards the outcoupling diffractive optical element ODO of the second image light guide 404. A third portion of the image-bearing light WI is transmitted through the incoupling diffractive optical element IDO1 of the second image light guide 404 and incident on the optical coupler 120 as described above. The third portion of the image-bearing light WI is output from the optical coupler 120 about the second axis A2 and incident on the second incoupling optical element IDO2 of the second image light guide 404. A portion of the image-bearing light WG3 incident on the second incoupling diffractive optical element IDO2 of the second image light guide 404 is diffracted and propagates via TIR towards the outcoupling diffractive optical element ODO of the second image light guide 404. A fourth portion of the image-bearing light WI is transmitted through the second incoupling diffractive optical element IDO2 of the second image light guide 404 and incident on the second incoupling diffractive optical element IDO2 of the first image light guide 402. A portion of the image-bearing light WG4 incident on the second incoupling diffractive optical element IDO2 of the first image light guide 402 is diffracted and propagates via TIR towards the outcoupling diffractive optical element ODO of the first image light guide 402. The image-bearing light WG1, WG2, WG3, WG4 incident on the outcoupling diffractive optical element ODO of the first and second image light guides 402, 404 is magnified and outcoupled towards the eye box as image-bearing light WO.

13 shows a perspective view of a display system 60 for viewing augmented reality using one or more image light guides of the present disclosure. The display system 60 is shown as an HMD with a right-eye optical system 64R with an image light guide 66R for the right eye. The display system 60 includes an image source 68, such as a picoprojector or similar device that can be excited to generate an image. In one embodiment, the display system 60 includes a left-eye optical system with one or more image light guides and a second image source. The generated images can be stereoscopic image pairs for three-dimensional display. The virtual image formed by the display system 60 can be viewed superimposed on real-world scene content viewed by the viewer through the image light guide 66R. Additional components familiar to those skilled in the art of augmented reality visualization can also be provided, such as one or more cameras mounted on the frame of the HMD for displaying scene content or tracking the viewer's gaze.

One or more features of the embodiments described herein may be combined to create additional embodiments not shown. Although various embodiments have been described in detail, it should be understood that they are presented by way of example and not limitation. It will be apparent to those skilled in the art that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the appended claims, and it is intended to include all changes that come within the meaning and range of equivalents thereof.

Claims (19)

a substrate operable to propagate an image-bearing light beam therethrough;
a first incoupling diffractive optical element formed along the substrate, the first incoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from an image source into the substrate in an angularly encoded manner and to transmit a second portion of the image-bearing light beam from the image source;
an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to expand an eyebox in at least one direction and to direct the image-bearing light beam away from the substrate in an angularly decoded manner;
a second incoupling diffractive optical element formed along the substrate, the second incoupling diffractive optical element operable to diffract a portion of the second portion of the image-bearing light beam into the substrate in an angularly encoded manner;
an optical coupler disposed along an axis of the image source and operable to direct the second portion of the image-bearing light beam to the second incoupling diffractive optical element;
an image light guide for transmitting a virtual image, comprising: An image light guide for transmitting a virtual image according to claim 1, wherein the first incoupling diffractive optical element is operable to diffract an image-bearing light beam incident from a first direction with greater efficiency than the second incoupling diffractive optical element, and the second incoupling diffractive optical element is operable to diffract an image-bearing light beam incident from a second direction with greater efficiency than the first incoupling diffractive optical element. The image light guide for transmitting a virtual image of claim 1 , wherein the first incoupling diffractive optical element and the second incoupling diffractive optical element comprise surface relief gratings. The image light guide for transmitting a virtual image according to claim 2, wherein the first incoupling diffractive optical element and the second incoupling diffractive optical element have grating features with tilted surface relief, the grating features of the second incoupling diffractive optical element being tilted at substantially 180 degrees with respect to the grating features of the first incoupling diffractive optical element. An image light guide for transmitting a virtual image as described in claim 2, wherein the grating features of the second incoupling diffractive optical element are symmetrical to the grating features of the first incoupling diffractive optical element. a substrate operable to propagate an image-bearing light beam therethrough;
a first incoupling diffractive optical element formed along the substrate and operable to diffract a first portion of the image-bearing light beam from an image source into the substrate in an angularly encoded manner and to transmit a second portion of the image-bearing light beam from the image source;
an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to expand an eyebox in at least one direction and to direct the image-bearing light beam away from the substrate in an angularly decoded manner;
a second incoupling diffractive optical element formed along the substrate and operable to diffract a portion of the second portion of the image-bearing light beam into the substrate in an angularly encoded manner;
an optical coupler disposed along an axis of the image source and operable to direct the second portion of the image-bearing light beam to the second incoupling diffractive optical element;
Equipped with
The optical coupler is
a first surface operable to transmit the image-bearing light beam incident at a first angle and to reflect the image-bearing light beam incident at a second angle;
a second surface operable to reflect said image-bearing light beam;
a third surface operable to reflect said image-bearing light beam;
an image light guide for transmitting a virtual image, comprising: 7. The image light guide for transmitting a virtual image of claim 6 , wherein the second surface of the optical coupler is symmetrical to the third surface of the optical coupler. 7. The image light guide for transmitting a virtual image of claim 6 , wherein the image-bearing light beam reflected by the second surface and incident on the first surface is reflected at the first surface by total internal reflection. 7. The image light guide for transmitting a virtual image of claim 6 , wherein the image-bearing light beam reflected by the third surface and incident on the first surface is transmitted through the first surface. 7. The image light guide for transmitting a virtual image of claim 6 , wherein the image-bearing light beam exits the light coupler laterally offset from where the image-bearing light beam enters the light coupler. 7. An image light guide for transmitting a virtual image as described in claim 6 , wherein the image-bearing light beam follows a path within the optical coupler that includes three reflections, and the image-bearing light beam exits the optical coupler at a mirror angle relative to the input image-bearing light beam. The image light guide for transmitting a virtual image of claim 6 , wherein the optical coupler includes two right angle prisms. a substrate operable to propagate an image-bearing light beam therethrough;
a first incoupling diffractive optical element formed along the substrate and operable to diffract a first portion of the image-bearing light beam from an image source into the substrate in an angularly encoded manner and to transmit a second portion of the image-bearing light beam from the image source;
an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to expand an eyebox in at least one direction and to direct the image-bearing light beam away from the substrate in an angularly decoded manner;
a second incoupling diffractive optical element formed along the substrate and operable to diffract a portion of the second portion of the image-bearing light beam into the substrate in an angularly encoded manner;
an optical coupler disposed along an axis of the image source and operable to direct the second portion of the image-bearing light beam to the second incoupling diffractive optical element;
a wave plate disposed between the optical coupler and the second incoupling diffractive optical element ;
An image light guide for transmitting a virtual image, wherein the waveplate is operable to rotate the polarization of the image-bearing light beam, the waveplate comprising a half waveplate or a quarter waveplate. a substrate operable to propagate an image-bearing light beam therethrough;
a first incoupling diffractive optical element formed along the substrate and operable to diffract a first portion of the image-bearing light beam from an image source into the substrate in an angularly encoded manner and to transmit a second portion of the image-bearing light beam from the image source;
an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to expand an eyebox in at least one direction and to direct the image-bearing light beam away from the substrate in an angularly decoded manner;
a second incoupling diffractive optical element formed along the substrate and operable to diffract a portion of the second portion of the image-bearing light beam into the substrate in an angularly encoded manner;
an optical coupler disposed along an axis of the image source and operable to direct the second portion of the image-bearing light beam to the second incoupling diffractive optical element;
Equipped with
the first portion of the image-bearing light beam coupled in through the first incoupling diffractive optical element corresponds to a first virtual image;
the second portion of the image-bearing light beam coupled in through the second incoupling diffractive optical element corresponds to a second virtual image;
the first and second virtual images are substantially identical;
An image light guide for transmitting a virtual image, wherein the substrate is rotated so that a surface of the substrate is positioned at an angle relative to a first surface of the optical coupler, whereby the first and second virtual images are aligned at a focus at infinity. a substrate operable to propagate an image-bearing light beam therethrough;
a first incoupling diffractive optical element formed along the substrate and operable to diffract a first portion of the image-bearing light beam from an image source into the substrate in an angularly encoded manner and to transmit a second portion of the image-bearing light beam from the image source;
an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to expand an eyebox in at least one direction and to direct the image-bearing light beam away from the substrate in an angularly decoded manner;
a second incoupling diffractive optical element formed along the substrate and operable to diffract a portion of the second portion of the image-bearing light beam into the substrate in an angularly encoded manner;
an optical coupler disposed along an axis of the image source and operable to direct the second portion of the image-bearing light beam to the second incoupling diffractive optical element;
Equipped with
the optical coupler comprises a first surface, a first portion of the first surface operable to transmit the image-bearing light beam incident on the first surface and a second portion of the first surface operable to reflect the image-bearing light beam incident on the first surface, the second portion of the first surface being a mirror surface;
the optical coupler further comprising a second surface operable to reflect the image-bearing light beam, and a third surface operable to reflect the image-bearing light beam;
the image-bearing light beam reflected by the second surface and incident on the second portion of the first surface is reflected by the first surface and incident on the third surface;
the image-bearing light beam reflected by the third surface and incident on the first surface is transmitted through the first surface; and an image light guide for transmitting a virtual image. an image source operable to project along an axis an image-bearing light beam corresponding to a virtual image, the pixels of the virtual image being focused at infinity;
a first substrate operable to propagate said image-bearing light beam;
a second substrate coupled to the first substrate and operable to propagate the image-bearing light beam;
Equipped with
each of the first and second substrates having a first incoupling diffractive optical element, a second incoupling diffractive optical element, and an outcoupling diffractive optical element operable to enlarge an eyebox in at least one direction and to direct at least a portion of the image-bearing light beam away from the substrate in an angularly decoded manner;
further comprising an optical coupler disposed along the axis ;
the optical coupler is disposed at least partially along a path of the image-bearing light beam transmitted through the first incoupling diffractive optical elements of the first and second substrates;
the optical coupler is operable to direct the image-bearing light beam to the second incoupling diffractive optical element of the second substrate;
the second incoupling diffractive optical element is operable to diffract a portion of the image-bearing light beam in an angularly encoded manner into the second substrate and to transmit and direct a portion of the image-bearing light beam towards the second incoupling diffractive optical element of the first substrate;
An image light guide system for transmitting a virtual image, wherein the second incoupling diffractive optical element of the first substrate is operable to diffract a portion of the image-bearing light beam into the first substrate in an angularly encoded manner. 17. The image light guide system for transmitting a virtual image of claim 16 , wherein the first incoupling diffractive optical element is operable as a transmissive diffractive optical element and the second incoupling diffractive optical element is operable as a reflective diffractive optical element. The optical coupler is
a first surface operable to transmit the image-bearing light beam incident at a first angle and to reflect the image-bearing light beam incident at a second angle;
a second surface operable to reflect said image-bearing light beam;
a third surface operable to reflect said image-bearing light beam;
17. The image light guide system for transmitting a virtual image according to claim 16 , comprising: a substrate operable to propagate an image-bearing light beam therethrough, the substrate having opposing first and second surfaces;
a first incoupling diffractive optical element formed along the substrate and disposed at the first surface or the second surface, the first incoupling diffractive optical element operable to diffract a first portion of the image-bearing light beam from an image source into the substrate in an angularly encoded manner and to transmit a second portion of the image-bearing light beam from the image source;
an outcoupling diffractive optical element formed along the substrate, the outcoupling diffractive optical element operable to expand an eyebox in at least one direction and to direct the image-bearing light beam away from the substrate in an angularly decoded manner;
a second incoupling diffractive optical element formed along the substrate and disposed at the first surface or the second surface, the second incoupling diffractive optical element operable to diffract a portion of the second portion of the image-bearing light beam into the substrate in an angularly encoded manner;
an optical coupler disposed along an axis of the image source and operable to direct the second portion of the image-bearing light beam to the second incoupling diffractive optical element;
Equipped with
An image light guide for transmitting a virtual image, wherein the second incoupling diffractive optical element is biased in a direction transverse to the propagation direction of the image-bearing light beam from the first incoupling diffractive optical element toward the outcoupling diffractive optical element.

Images